The present invention relates to an apparatus for measuring a seat weight, including the weight of a passenger sitting on a vehicle seat. Particularly, the present invention relates to a seat weight measuring apparatus which has enough strength against load in a direction in which a rear side of the vehicle seat is lifted.
Automobiles are equipped with seat belt devices and airbag devices to secure safety for passengers in the automobiles. In recent years, there is a trend for controlling the actions of these safety devices depending on the weight (body weight) of a passenger in order to improve the performance of seat belt devices and/or airbag devices. For example, the amount of gas for deploying the airbag, the airbag inflating speed, or the pretension load of the seat belt may be adjusted depending on the weight of the passenger. For that purpose, it is necessary to somehow measure the weight of the passenger sitting on the seat.
One example for achieving this objective is a seat weight measuring apparatus employing strain gauges as load sensors. Load sensors to be used for this purpose are required to have both sufficiently high accuracy of detection and sufficient fracture strength. The accuracy of detection required for the load sensor for a load in the gravitational direction is a level enabling a load variation of about 100 g to be detected. It is required that the accuracy is not affected when a load of 100 kg is applied in any direction other than the gravitational direction. On the other hand, as for the strength of the load sensor, it is required that the sensor is not broken even when it is subjected to a large load in the event of a vehicle collision. Examples of load sensors satisfying the above mentioned conditions are disclosed in Japanese Patent Unexamined Publication No. H11-304579, Japanese Patent Unexamined Publication No. H11-351952, Japanese Patent Unexamined Publication No. 2000-258233, Japanese Patent Unexamined Publication No. 2000-122068, and Patent Unexamined Publication No. 2001-12998, each of which is hereby incorporated by reference herein.
Further, large negative G may be applied to a vehicle body so as to create a moment lifting up the rear side of a vehicle seat in the event of a vehicle collision. Accordingly, one object of the present invention is to provide a seat weight measuring apparatus having enough strength against load in a direction in which the rear side of the vehicle seat is lifted.
Another object of the present invention is to provide a seat weight measuring apparatus that does not generate noise that hurts passengers' ears.